Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$72.88	6.738%	$77.7907	$77.79	$77.80	$77.80
Purchase #2	$92.62	13.795%	$105.3969	$105.40	$105.40	$105.40
Purchase #3	$206.25	7.753%	$222.2406	$222.24	$222.25	$222.20
Purchase #4	$156.90	5.102%	$164.905	$164.91	$164.90	$164.90
Purchase #5	$45.40	10.807%	$50.3064	$50.31	$50.30	$50.30
Purchase #6	$93.52	3.184%	$96.4977	$96.50	$96.50	$96.50
Purchase #7	$213.86	4.411%	$223.2934	$223.29	$223.30	$223.30
7 purchase totals =	$881.43		$940.4307	$940.44	$940.45	$940.40